Intelligibility of the Adaptive Multi-Rate Speech Coder in Emergency-Response Environments

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Abstract: This report describes speech intelligibility testing conducted on the Adaptive Multi-Rate (AMR) speech coder in several different environments simulating emergency response conditions and especially fireground conditions. The intelligibility testing protocol was the Modified Rhyme Test (MRT). Conditions included background noises of various types, as well as a mask associated with a self-contained breathing apparatus. Analog FM radio transmission and Project 25 digital radio transmission were also included in the test as reference points. Test participants were persons employed as first responders in public safety fields. Through statistical analysis of 26,900 MRT trials we are able to draw conclusions on speech intelligibility for AMR speech coding relative to analog and digital radio reference points for five different operating environments.